1. Field of the Invention
This invention relates to the closure of large vessels which may operate under pressure and at high temperature.
2. Description of the Prior Art
The most common method for mounting doors, covers or other closure devices on such large vessels has been by bolting them to flanges on the vessel opening. Sealing, where required, is usually by use of various gaskets or O-rings. Removal and replacement of a bolted cover is a time-consuming operation. High temperature or pressure vessel closures are typically held in place by numerous bolts or studs and nuts. Removal of these bolts or nuts must generally be done by operators on site and thus it is sometimes necessary to wait for the vessel to cool before the closure can be removed.
Another method sometimes used to remove such a vessel cover involves the placement of some type of strong back or frame over the back of the closure and attaching the frame to the vessel thereby pressing the closure itself onto the opening. Such frames can be hinged or otherwise attached to reduce the number of bolts or other attachment devices necessary to hold the closure on the vessel opening. This method requires the sacrifice of some of the rigidity and sealing ability found in the aforementioned bolted flange system. Numerous cycles of operation can cause the cover itself to become warped or cause the sealing devices used to deteriorate so that a successful design must allow for these increased tolerances. Where the temperatures and pressures encountered will allow their use, inflatable seals are sometimes incorporated into either of these types of vessel closure designs in order to accommodate the warping and deterioration that will take place.
A device disclosed in U.S. Pat. No. 3,819,479 exhibits inflatable seals which can aid in sealing between the vessel flange and the closure plug and the flange of the plug. Some of these seals can also be inflated in order to lift the plug itself and allow its movement. This design incorporates a variation of the bolted flange with the plug assembly being bolted in place by use of a collar. The device disclosed in U.S. Pat. No. 871,421 exhibits an inflatable tube which exerts a force against a door and a door frame to seal the door against the vessel. The door is held in place by a separate locking device. The inflatable tube here is used to position the door for sealing by other devices rather than performing the sealing function itself. The invention disclosed in U.S. Pat. No. 3,632,303 exhibits a pressure hose which can be pressurized to exert force via a lever bar to force the closure against a seal. The attachment of the closure to the vessel is achieved by a variation of the normal bolting method. Local operation by hand is essential in attaching the closure to the vessel. The invention disclosed by U.S. Pat. No. 3,500,584 exhibits an inflatable seal which positions the closure against another seal with attachment of the closure being by means of a bolted apparatus. These and similar devices all suffer from the disadvantage of requiring local hand operation to attach or remove the closure and sometimes they sacrifice the strength of a bolted flange in order to reduce removal time, resulting in warpage or seal failure.